The present invention relates to a sintered compact used in manufacture of a magnetic thin film for heat-assisted magnetic recording media, and a manufacturing method thereof.
In the field of magnetic recording represented by hard disk drives, a material based on a ferromagnetic metal Co, Fe or Ni is used as a material for a magnetic thin film in a magnetic recording medium. For example, Co—Cr based or Co—Cr—Pt based ferromagnetic alloys having Co as a main component are used for magnetic thin films in hard disks employing the longitudinal magnetic recording system. Further, a composite material composed of a Co—Cr—Pt based ferromagnetic alloy having Co as a main component, and non-magnetic inorganic grains is often used for a magnetic thin film in a hard disk employing the recently-commercialized perpendicular magnetic recording system. In many cases, the above magnetic thin films are manufactured by sputtering a target consisting primarily of the above materials using a DC magnetron sputtering equipment in view of high productivity.
The recording density of a hard disk is rapidly increasing every year, and a current surface density of 600 Gbit/in2 may reach 1 Tbit/in2 in the future. If the recording density reaches 1 Tbit/in2, then the size of a recording bit becomes smaller than 10 nm. In that case, a problem of superparamagnetization due to thermal fluctuation may arise. Further, it is predicted that materials for magnetic recording media currently used, for example, materials in which magnetocrystalline anisotropy is enhanced by adding Pt to a Co—Cr based alloy, will be insufficient. This is because magnetic grains with a size of 10 nm or less stably showing ferromagnetic behavior are required to have higher magnetocrystalline anisotropy.
In view of the above reason, a FePt phase having the L10 structure has gathered much attention as a material for ultrahigh density recording media. A FePt phase is a promising material suitable for applications of magnetic recording media since it has high magnetic crystalline anisotropy as well as excellent corrosion resistance and oxidation resistance. Meanwhile, in order to use a FePt phase as a material for ultrahigh density recording media, a technology needs to be developed which allows regularly-arranged FePt grains to be dispersed as densely as possible in an aligned orientation and in a magnetically isolated manner.
For these reasons, a granular structure magnetic thin film, in which FePt magnetic grains having the L10 structure are isolated through the interposition of non-magnetic materials such as an oxide and carbon, has been proposed for a magnetic recording medium of a next generation hard disk adapted for the heat-assisted magnetic recording system. The granular structure magnetic thin film has a structure in which magnetic grains are magnetically insulated from each other through the interposition of nonmagnetic substances. In general, deposition of a granular structure magnetic thin film having a Fe—Pt phase is performed using a Fe—Pt based sintered compact sputtering target.
With regard to a sputtering target of Fe—Pt based magnetic material sintered compact, the present inventors previously have disclosed a technology for a ferromagnetic sputtering target, which is configured from a magnetic phase such as an Fe—Pt alloy, and a nonmagnetic phase that decouples the magnetic phase, and in which a metal oxide is used as one of the nonmagnetic phase materials (Patent Literature 1).
In addition, Patent Literature 2 discloses a sputtering target for depositing a thin-film magnetic recording medium formed from a sintered compact having a structure in which C phases are dispersed in a FePt alloy phase. Patent Literature 3 discloses a sputtering target for depositing a thin-film magnetic recording medium comprising a SiO2 phase, a FePt alloy phase and an interdiffusion phase. Further, Patent Literature 4 discloses a Fe—Pt based ferromagnetic material sputtering target comprising Pt, SiO2, Sn, and the remainder being Fe. Patent Literature 5 discloses a sputtering target for depositing a magnetic recording film, in which a peak intensity ratio of the (011) plane of quartz is 1.40 or more relative to a background intensity in X-ray diffraction.
Hexagonal BN (a compound of boron and nitrogen) as the above non-magnetic material shows excellent performance as a lubricant. The compound, however, is difficult to be used for the production of a high density sintered compact because sinterability is poor when used as a raw material for powder metallurgy. In a case where the density of a sintered compact is low as described above, defects such as cracks and chipping may occur when processing the sintered compact into a target, causing a problem of a reduced yield. Further, low density may result in a large number of voids created in a target. These voids may cause abnormal electric discharge, which, in turn, may generate particles (dust which will adhere on a substrate) during sputtering, causing a problem of a reduced product yield.    Patent Literature 1: WO2012/029498    Patent Literature 2: Japanese Patent Application Laid-Open No. 2012-102387    Patent Literature 3: Japanese Patent Application Laid-Open No. 2011-208167    Patent Literature 4: WO2012/086578    Patent Literature 5: Japanese Patent No. 5009447